Disk Rotation Research Articles

Unstable accretion in TW Hya: 3D simulations and comparisons with observations

Abstract We investigate the origin of photometric variability in the classical T Tauri star TW Hya by comparing light curves obtained by TESS and ground-based telescopes with light curves created using three-dimensional (3D) magnetohydrodynamic (MHD) simulations. TW Hya is modeled as a rotating star with a dipole magnetic moment, which is slightly tilted about the rotational axis. We observed that for various model parameters, matter accretes in the unstable regime and produces multiple hot spots on the star’s surface, which leads to stochastic-looking light curves similar to the observed ones. Wavelet and Fourier spectra of observed and modeled light curves show multiple quasiperiodic oscillations (QPOs) with quasiperiods from less than 0.1 to 9 days. Models show that variation in the strength and tilt of the dipole magnetosphere leads to different periodograms, where the period of the star may dominate or be hidden. The amplitude of QPOs associated with the stellar period can be smaller than that of other QPOs if the tilt of the dipole magnetosphere is small and when the unstable regime is stronger. In models with small magnetospheres, the short-period QPOs associated with rotation of the inner disc dominate and can be mistaken for a stellar period. We show that longer-period (5-9 days) QPOs can be caused by waves forming beyond the corotation radius.

A Precessing-Coin-like Rotary Actuator for Distal Endoscope Scanners: Proof-of-Concept Study.

This paper presents, for the first time, a rotary actuator functionalized by an inclined disc rotor that serves as a distal optical scanner for endoscopic probes, enabling side-viewing endoscopy in luminal organs using different imaging/analytic modalities such as optical coherence tomography and Raman spectroscopy. This scanner uses a magnetic rotor designed to have a mirror surface on its backside, being electromagnetically driven to roll around the cone-shaped hollow base to create a motion just like a precessing coin. An optical probing beam directed from the probe's optic fiber is passed through the hollow cone to be incident and bent on the back mirror of the rotating inclined rotor, circulating the probing beam around the scanner for full 360° sideway imaging. This new scanner architecture removes the need for a separate prism mirror and holding mechanics to drastically simplify the scanner design and thus, potentially enhancing device miniaturization and reliability. The first proof-of-concept is developed using 3D printing and experimentally analyzed to reveal the ability of both angular stepping at 45° and high-speed rotation up to 1500 rpm within the biologically safe temperature range, a key function for multimodal imaging. Preliminary optical testing demonstrates continuous circumferential scanning of the laser beam with no blind spot caused by power leads to the actuator. The results indicate the fundamental feasibility of the developed actuator as an endoscopic distal scanner, a significant step to further development toward advancing optical endoscope technology.

Particle size distribution of Japanese cedar chip converted from boards using a disc chipper and its relationships with disc rotation speed and board feed speed

The effects of disc chipper rotation speed and raw material feed speed on the particle size distribution of wood chips produced were investigated to develop an efficient technique for producing ideal sized chips for the stable operation of combined heat and power plants. The particle size distribution of wood chips was measured using a screening method and approximated to a Rosin–Rammler distribution to calculate the median of the chip. The results suggest that chip size decreased as the rotation speed increased from 560 to 720 rpm, but no clear effect of feed speed on the chip size was observed. The Rosin–Rammler equation was found to be appropriate to explain the size distribution of wood chips. Two types of screening sieves, woven wire mesh sieve and perforated plate sieve, were used for the screening. It was found that the woven wire mesh sieve may underestimate the size of the chip, although the Rosin–Rammler equation derived from the woven wire mesh sieve was able to be converted to the equation for the perforated plate sieve.

Interactional Aerodynamics of Single Main Rotor Helicopters in Steady Autorotation

Autorotation is an edge case flight regime where, instead of being powered by an engine, a rotorcraft is powered purely by the air moving up through the main rotor as the vehicle descends. In this paper, a full-vehicle UH-60A helicopter is simulated in steady autorotation using both the flight dynamics (FD) code HeliUM-A and the computational fluid dynamics/computational structural dynamics (CFD/CSD) solver CREATE-AVTM Helios. The CFD/CSD simulations model the full-vehicle geometry and are trimmed to an autorotative state that is representative of how the aircraft flies in practice. Despite significant differences in the predicted airloads, both FD and CFD/CSD predictions of the vehicle’s autorotational descent rate were in excellent agreement with available flight test data. CFD/CSD analysis further examined mutual interactions between the helicopter’s rotors and various airframe components. The airframe plays a critical role in determining the aircraft’s autorotational descent rate and its shed wake creates regions of loading loss in the rotor disk. On the other hand, the main rotor induces significant unsteadiness on the airframe loading and creates an effective downforce on the fuselage and stabilator.

Three-dimensional numerical simulation of the single-wafer spin rinsing process using OpenFOAM

Abstract To investigate the rinsing process in single-wafer spin cleaning, we simulated a three-dimensional unsteady replacement process in which pure water from a nozzle replaced a chemical solution on a rotating disk. The simulation used a two-phase flow solver provided by OpenFOAM combined with our modified approach for advective–diffusive transport of the chemical concentration in the liquid phase. We analyzed the effect of the nozzle position by performing computations with water supplied on- and off-axes. In the axisymmetric configuration, the solution displacement near the disk edge was challenging; in the nonaxisymmetric configuration, it was difficult around the disk center. Axisymmetric two-dimensional computations were also conducted to examine the replacement speed. The replacement of trace concentrations was strongly dependent on shear flow-driven concentration gradients, which facilitate molecular diffusion. The replacement rate was accelerated by the steepening of shear flow due to jet stagnation pressure and centrifugal forces from the disk rotation.

Enhanced rotational diffusion and spontaneous rotation of an active Janus disk in a complex fluid.

Active colloids and self-propelled particles moving through microstructured fluids can display different behavior compared to what is observed in simple fluids. As they are driven out of equilibrium in complex fluids they can experience enhanced translational and rotational diffusion as well as instabilities. In this work, we study the deterministic and the Brownian rotational dynamics of an active Janus disk propelling at a constant speed through a complex fluid. The interactions between the Janus disk and the complex fluid are modeled using a fluctuating advection-diffusion equation, which we solve using the finite element method. Motivated by experiments, we focus on the case of a complex fluid comprising molecules that are much smaller than the size of the active disk but much bigger than the solvent. Using numerical simulations, we elucidate the interplay between active motion and fluid microstructure that leads to enhanced rotational diffusion and spontaneous rotation observed in experiments employing Janus colloids in polymer solutions. By increasing the propulsion speed of the Janus disk, the simulations predict the onset of a spontaneous rotation and an increase of the rotational diffusion coefficient by orders of magnitude compared to its equilibrium value. These phenomena depend strongly on the number density of the constituents of the complex fluid and their interactions with the two sides of the Janus disk. Given the simplicity of our model, we expect that our findings will apply to a wide range of active systems propelling through complex media.

Vortex convective flows formed during the melting of ice in single-component media

The results of theoretical and experimental studies of convective vortex currents formed during ice melting, as well as physical modeling of the phenomenon of spontaneous rotation of an ice disk on the water surface, are presented. It is shown that the cause of the observed movements on the surface of initially quiescent water is a cellular convective flow generated by the process of ice melting at the lower boundary of the disk, and a new physical model of such rotation is constructed.

Implications of optic disc rotation in the visual field progression of myopic open-angle glaucoma.

To investigate the relationship between the characteristics of optic disc rotation and visual field (VF) progression in patients with myopic open-angle glaucoma (OAG). We included 53 eyes from 53 myopic OAG patients who were followed-up over a 3-year period. The characteristics of optic disc rotation including the degree of optic disc rotation, direction of optic disc rotation, and optic disc rotation-VF defect correspondence were investigated. The rates of global and regional VF progression were compared with different characteristics of optic disc rotation. Thirty-seven eyes (69.8%) showed inferior optic disc rotation and 41 (77.4%) eyes showed optic disc rotation-VF defect correspondence. The inferiorly rotated optic discs with corresponding superior VF defect had faster VF progression in the superior peripheral region (P = 0.028) and superiorly rotated optic discs with corresponding inferior VF defect had faster VF progression in the inferior peripheral region (P = 0.031). The VF progression was restricted to the superior hemifield in the eyes with inferiorly rotated optic discs and corresponding superior VF defects. In myopic OAG patients, the direction of optic disc rotation might predict faster VF progression in the corresponding peripheral region.

Rotation of the Milky Way halo in the solar neighborhood based on GAIA DR3 catalog

The rotation of the Milky Way halo in the solar neighborhood is investigated using kinematic data from the GAIA DR3 catalog for RR Lyrae variable stars with parallax errors of less than 20%. Two criteria were used for selecting halo stars — kinematic and spatial. In both approaches, we confirm the existence of weak rotation of the halo in the direction opposite to the rotation of the Galactic disk with velocities of 4.08 ± 2.19 km/s for the kinematic criterion and 9.49 ± 2.59 km/s for the spatial criterion.

Unveiling VVV/WISE Mira variables on the far side of the Galactic disk

Context. The structure and kinematics of the Milky Way disk are largely inferred from the solar vicinity. To gain a comprehensive understanding, it is essential to find reliable tracers in less explored regions such as the bulge and the far side of the disk. Mira variables, which are well studied and bright standard candles, offer an excellent opportunity to trace intermediate and old populations in these complex regions. Aims. We aim to isolate a clean sample of Miras in the VISTA Variables in the Vía Láctea survey using Gaussian process algorithms. This sample will be used to study intermediate and old age populations in the Galactic bulge and far disk. Methods. Near- and mid-infrared time-series photometry were processed using Gaussian Process algorithms to identify Mira variables and model their light curves. We calibrated selection criteria with a visually inspected sample to create a high-purity sample of Miras, integrating multiband photometry and kinematic data from proper motions. Results. We present a catalog of 3602 Mira variables. By analyzing photometry, we classify them by O-rich or C-rich surface chemistry and derive selective-to-total extinction ratios of AKs/E(J − Ks) = 0.471 ± 0.01 and AKs/E(H − Ks) = 1.320 ± 0.020. Using the Mira period-age relation, we find evidence supporting the inside-out formation of the Milky Way disk. The distribution of proper motions and distances aligns with the Galactic rotation curve and disk kinematics. We extend the rotation curve up to RGC ~ 17 kpc and find no strong evidence of the nuclear stellar disk in our Mira sample. This study constitutes the largest catalog of variable stars on the far side of the Galactic disk to date.

Methodology for Modeling Nonlinear Thermomechanical Response With Wear at High-Speed Interactions: Application to a Pin–Disk Configuration

Abstract An aircraft engine is a complex structure for which some components can come into contact at high speed. Modeling this behavior is very complex as multiple physics must be considered. State-of-the-art methodologies usually account for permanent contact and thermal modeling. In this paper, a new approach is proposed and embeds various phenomena such as nonregular and nonlinear contact mechanics, surface rubbing, wear, and nonlinear heat transfer. A nonlinear version of Moreau–Jean algorithm is employed to compute the transient response of the system and to capture accurately the contact dynamics. Moreover, the full nonlinear coupling between the dynamics and the heating process is taken into account through both a semi-analytical formulation and the finite element (FE) method. At the contact interface, heat flux is generated by dry rubbing and flows into both interacting bodies. The heat flux partition is evaluated thanks to a coefficient that depends on the material properties of the solids in contact. The proposed method also accounts for the adhesive wear between the solids through an energetic approach. This methodology is applied to an academic, yet realistic, disk connected to a rotor shaft that is free to move axially and to rotate around its revolution axis. Gyroscopic effects and variation of the rotation velocity are included leading to a full nonlinear mechanical behavior. The disk undergoes aerodynamic load moving it to contact with a clamped free pin. The rotor shaft and the pin are both modeled as one-dimensional (1D) elastic bodies, while the rotor disk is assumed to be rigid. Through this example, the developed strategy shows its potential to compute the complete transient highly nonlinear response of the breaking phenomenon, in an acceptable time simulation.

Disk Kinematics at High Redshift: DysmalPy’s Extension to 3D Modeling and Comparison with Different Approaches

Spatially resolved emission-line kinematics are invaluable for investigating fundamental galaxy properties and have become increasingly accessible for galaxies at z ≳0.5 through sensitive near-infrared imaging spectroscopy and millimeter interferometry. Kinematic modeling is at the core of the analysis and interpretation of such data sets, which at high z present challenges due to the lower signal-to-noise ratio (S/N) and resolution compared to the data of local galaxies. We present and test the 3D fitting functionality of DysmalPy, examining how well it recovers the intrinsic disk rotation velocity and velocity dispersion, using a large suite of axisymmetric models, covering a range of galaxy properties and observational parameters typical of z ∼ 1−3 star-forming galaxies. We also compare DysmalPy’s recovery performance to that of two other commonly used codes, GalPak 3D and 3D Barolo, which we use in turn to create additional sets of models to benchmark DysmalPy. Over the ranges of S/N, resolution, mass, and velocity dispersion explored, the rotation velocity is accurately recovered by all tools. The velocity dispersion is recovered well at high S/N, but the impact of methodology differences is more apparent. In particular, template differences for parametric tools and S/N sensitivity for the nonparametric tool can lead to differences of up to a factor of 2. Our tests highlight and the importance of deep, high-resolution data and the need for careful consideration of (i) the choice of priors (parametric approaches); and (ii) the masking (all approaches); and (iii), more generally, the evaluating of the suitability of each approach to the specific data at hand. This paper accompanies the public release of DysmalPy.

Dynamics analysis of rotor in disc centrifuge for separation of bioengineering

In order to reveal the influence of gyroscope effect and structure parameters on the modal frequency and critical speed of the rotor system in disc centrifuge for separation of bioengineering. Based on the rotor rigid body dynamics, the fixed-point gyroscope motion of the rotating spindle of the disc centrifuge was analyzed. Establishing a finite element dynamic model for the rotor system of a disc centrifuge, taking into account the gyroscopic moment caused by the rotational inertia of the rotor disk and the elastic support of the bearings. We calculated the gyroscopic moment and the analytical expression of critical speed. Analyzing the quantitative relationship between the gyroscope effect, bearing support stiffness, drum material density and the critical speed of the rotor system. The results show that the calculated value of finite element is close to the measured value. The influence of gyroscopic force on the vibration characteristics of rotor system for dish centrifuge cannot be ignored. The critical speeds of the rotor system increase with the increase of elastic support stiffness, while the first critical speed decreases with the increase of drum density, but the second critical speed increases with the increase of drum density. These studies provide a theoretical reference for the dynamic response, structural design and dynamic balance of disc centrifuge.

FLOW AND HEAT TRANSFER IN A ROTATING DISC CAVITY WITH AXIAL THROUGHFLOW AT HIGH SPEED CONDITIONS

FLOW AND HEAT TRANSFER IN A ROTATING DISC CAVITY WITH AXIAL THROUGHFLOW AT HIGH SPEED CONDITIONS

High order moment conserving method of classes in CFD code

Abstract Dispersed multiphase flows are widely present in the majority of chemical process industry equipment. For the purpose of design, optimization, and scale up of these industrial systems, robust, accurate and fast simulation methods are needed, especially when coupling computational fluid dynamics (CFD) with population balance models (PBM). In this work, the high-order moment conserving method of classes (HMMC) is implemented and tested within the commercial CFD software of ANSYS Fluent with two simple well-defined test cases and a realistic 3D simulation of rotating disc (RDC) extractor. Firstly, a zero-dimensional PBM with well-mixed assumption and no convection was solved for a single computational cell in Fluent to verify the implementation in comparison with a simple reactor model in MATLAB. Secondly, the convection was considered by solving a one-dimensional PBM for three computational cells side by side in Fluent and compared with an equivalent three staged reactor model in MATLAB. Eventually, realistic 3D RDC simulations were conducted to fully couple the HMMC and CFD in Fluent. The implementation of HMMC was compared to predictions with other state-of-the-art PBM solution methods, e.g., the quadrature method of moments (QMOM) and the fixed pivot technique (FPT) in Fluent and MATLAB platforms. The implementation of the HMMC in Fluent platform was straightforward with no additional challenges. The verification shows that the HMMC approach is robust and efficient for polydispersed multiphase CFD simulations.

Modeling and Dynamic Analysis of Double-Row Angular Contact Ball Bearing–Rotor–Disk System

This article presents a general numerical method to establish a mathematical model of a bearing–rotor–disk system. This mathematical model consists of two double-row angular contact ball bearings (DRACBBs), a rotor and a rigid disk. The mathematical model of the DRACBB is built on the basis of elastic Hertz contact by adopting the Newton Raphson iteration method, and three different structure forms are taken into account. The rotor is modeled by employing a finite element method in conjunction with Timoshenko beam theory, and the rigid disk is modeled by applying the lumped parameter method. The mathematical model of the bearing–rotor–disk system is constructed by the coupling of the bearing, rotor and disk, and the dynamic response of the bearing–rotor–disk system can be solved by employing the Newmark-β method. The validation of the above mathematical model is demonstrated by comparing the proposed results with the results from the existing literature and finite element software. The dynamic characteristics of the DRACBBs and the dynamic response of the bearing–rotor–disk system are investigated by parametric study. A dynamic characteristic analysis of the DRACBB is conducted to ensure the optimal structure form of the DRACBB under complex external loads, and it can provide a reference for the selection of the structural forms of DRACBBs.

Влияние направления печати на характер износа PLA-биоматериала, полученного методом FDM: исследование для имплантата тазобедренного сустава

Introduction: hip joint replacement surgery involves replacing the damaged joint with an implant that can re-create the joint's articulation functionality. 3D printing technology is more promising than the traditional manufacturing process when it comes to producing more complex parts and shapes. The goal of the current research project is to determine how quickly biomaterial implant can be manufactured using 3D printing for hip-joint replacement by studying the wear rate of parts manufactured using different printing orientations. Although there are several additive manufacturing technologies, fuse deposition modeling (FDM) technology has had a significant impact on healthcare, automotive industry, etc. This is mainly due to the adaptability of different polymer-based composite materials and its cost-effectiveness. Such 3D printed polymers need to be further studied to evaluate the wear rate depending on different 3D printing orientations. Polylactic acid (PLA) biomaterials were extensively studied to determine its suitability for use as hip joint materials. Purpose of the work: in this work, an experimental study was carried out on the effect of printing orientation on dry sliding wear of a polylactic acid (PLA) material obtained by fused deposition modeling (FDM) technology using the pin-on-disk (SS 316) scheme. In addition, experimental and empirical models are developed to predict the performance taking into account the influence of load and sliding speed. Grey relational analysis was used to determine the optimal parameters. The methods of investigation: the FDM printing was used to manufacture pins using different printing orientations. Printing direction refers to printing at angles of 0°, 45°, and 90°, while all other 3D printing parameters remained unchanged. Wear testing was performed using the pin-on-disk kinematic scheme. During the experiments, the normal pin load and disk rotation speed were varied. The experiments were methodically designed to study the effect of input parameters on the specific wear rate. About 13 experiments were conducted for each printing orientation with a friction path of 4 kilometers, in the load range of 400–800 N, at a sliding speed of 450–750 rpm. Result and discussion: the study provides important results especially regarding the direction of 3D printing of components. It was found that the lowest sliding wear was observed for the pin printed at an angle of 0°, while slightly higher wear was observed for the pin printed at an angle of 90°. The layer bonding in the pin printed at an angle of 45° deformed under higher load, mainly due to an increase in temperature. The low bond strength in the pin printed at an angle of 45° resulted in high sliding wear. The optimal result was achieved at a sliding speed of 451 rpm and a load of 600 N. The results of the study are very useful for choosing materials for 3D printing of biomedical implants, medical and industrial products.

Numerical investigation on aerodynamic noise of rigid coaxial rotor in forward flight with lift-offset

A computational fluid dynamics (CFD) solver based on Reynolds-averaged Navier–Stokes (RANS) equations and high-efficiency trim model is used to simulate the unsteady aerodynamics of coaxial rotor. Farassat 1 A equations are adopted for predicting rotor far-field aerodynamic noise. Forward flight cases of a two-bladed rigid coaxial rotor in different advance ratios and lift-offsets (LOS) are conducted. Sound pressure histories of different observation points and noise radiation maps are analyzed. Results indicate that, the intensity of rotor thickness noise moves towards the advancing side in the rotor disk plane, with the increase of advance ratio. Due to the superposition effect, the thickness noise of coaxial rotor is symmetrical, which is different with the single rotor. At low advance ratio, loading noise of the rigid coaxial rotor is enhanced near the blade-crossing azimuths caused by the unsteady interaction of the twin rotors. The enhancement turns weak with the increase of advance ratio. At high advance ratio, increasing LOS tends to enhance the rotor-self BVI noise, while weakening the inter-rotor interaction noise. At certain flight states, appropriate LOS can reduce the overall noise radiation intensity of rigid coaxial rotor.

The Effect of Ultrasonic Vibration on the 3D Printing Fabrication and Grinding Performance of Structured CBN Grinding Wheel.

The abrasives of traditional grinding wheels are usually randomly arranged on the substrate, reducing the number of effective abrasive grains involved in the machining during the grinding process. However, there are some problems such as uneven distribution of chip storage space, high grinding temperature, and easy surface burn. In trying to address this issue, an ultrasonic vibration 3D printing method is introduced to fabricate the structured CBN (Cubic Boron Nitride) grinding wheel. The effects of the fabricated process parameters, overlap rate, scanning path, and ultrasonic amplitude were analyzed. The effects of laser power, scanning speed, and powder disk rotation speed on the topography of the printing layer were analyzed by orthogonal tests. The obtained data were input into the GA-BP (Genetic Algorithm-Back Propagation) neural network for training, and the trained model was utilized to derive the optimal process parameters. Then, the experiments were carried out to optimize the overlap rate and the scanning path. The effect of ultrasonic vibration amplitude on the surface topography and the microhardness of the printing layer was observed and investigated. The structured CBN grinding wheels were fabricated using the optimal parameters, and the performance of the grinding wheels was evaluated. The workpiece surface roughness ground by the grinding wheel fabricated with ultrasonic vibration was smaller than that without ultrasonic vibration, and a better workpiece surface quality was obtained.

Equilibrium dynamical models in the inner region of the Large Magellanic Cloud based on Gaia DR3 kinematics

Context. The Large Magellanic Cloud (LMC) contains complex dynamics driven by both internal and external processes. The external forces are due to tidal interactions with the Small Magellanic Cloud and the Milky Way, while internally its dynamics mainly depend on the stellar, gas, and dark matter mass distributions. Despite this complexity, simple physical models often provide valuable insights into the primary driving factors. Aims. We used Gaia Data Release 3 (DR3) to explore how well equilibrium dynamical models based on the Jeans equations and the Schwarzschild orbit superposition method are able to describe the LMC’s five-dimensional phase-space distribution and line-of-sight (LOS) velocity distribution, respectively. In the Schwarzschild model, we incorporated a triaxial bar component for the first time and derived the LMC’s bar pattern speed. Methods. We fit comprehensive Jeans dynamical models to all Gaia DR3 stars with proper motion and LOS velocity measurements found in the footprint of the VISTA near-infrared survey of the Magellanic System using a discrete maximum likelihood approach. These models are very efficient at discriminating genuine LMC member stars from Milky Way foreground stars and background galaxies. They constrain the shape, orientation, and enclosed mass of the galaxy under the assumption of axisymmetry. We used the Jeans model results as a stepping stone to more complex two-component Schwarzschild models, which include an axisymmetric disc and a co-centric triaxial bar, which we fit to the LMC Gaia DR3 LOS velocity field using a χ2 minimisation approach. Results. The Jeans models describe the rotation and velocity dispersion of the LMC disc well, and we find an inclination angle of θ = 25.5° ±0.2°, line of nodes orientation of ψ = 124° ±0.4°, and an intrinsic thickness of the disc of q0d = b/a = 0.23 ± 0.01 (minor to major axis ratio). However, bound to axisymmetry, these models fail to properly describe the kinematics in the central region of the galaxy dominated by the LMC bar. We used the derived disc orientation and the Gaia DR3 density image of the LMC to obtain the intrinsic shape of the bar. Using these two components as input to our Schwarzschild models, we performed orbit integration and weighting in a rotating reference frame fixed to the bar, deriving an independent measurement of the LMC bar pattern speed of Ω = 11 ± 4 km s−1 kpc−1. Both the Jeans and Schwarzschild models predict the same enclosed mass distribution within a radius of 6.2 kpc of ∼ 1.4 × 1010 M⊙.